1. Field of the Invention
The present invention relates generally to a switch device. More particularly, the invention relates to a switch device adapted to be attached to a steering wheel of a vehicle.
2. Description of Relevant Art
In recent years, a control arrangement has been developed for controlling the operation of a variety of equipment installed in a motor vehicle, particularly the various electrical equipment therein such as a radio or other audio devices before which the will of a driver or passenger in a vehicle takes an extreme preference, which arrangement provides a control device, including a computer or microprocessor, to operate such electrical equipment in accordance with a control signal from the control device. According to the arrangement, an associated control system has a simplified structure and a reduced amount of electrical wiring, while in order to output the necessary control signal from the simplified control device it is required that the driver or passenger supply the control device with an operational signal via through an electrical operation switch.
Conventionally, for the arrangement of such a control device and an operational switch in a vehicle, there are employed various layout systems: exemplarily, there is one in which on one hand a control device is mounted on a stationary part of the vehicle such as its body and, on the other hand, an operation switch is installed in a mobile part of the vehicle such as a steering wheel; in consideration of the accessibility for operation.
For a switch device following this type of arrangement, it is inherently necessary to provide a special constitution or structure for connections; such as of a signal line and a power line; between the control device mounted on the vehicle body as a stationary part and the operational switch mounted on the steering wheel as a mobile part.
Exemplarily, of such connections, there have been already devised a number of implements such as an electrical brush and a slip ring.
In this respect, however, when applied as a connection for the mobile operation switch to the stationary control device, such a connection system as using the conventional implements discussed alone may encounter some troubles. Exemplarily, the electric brush may be oxidized at a contact surface thereof, giving rise to a poor contact condition, gradually and resulting in failing stable performance of the entire switch device.
To overcome such problems to a certain extent, there have been already proposed some switch devices which employ a signal line of an optical transmission system, while still retaining the conventional problems attendant the connection of a power line.
As an improvement of such switch devices employing an optical transmission system, there is disclosed a steering switch device in Japanese Patent Lay-Open Print No. 59-25439, in which an optical operation switch only is provided as a mobile part on a steering wheel; and in which an optical operation signal is fed to a control device which is mounted at the side of a stationary part.
More particularly, in this steering switch device, a light beam of a predetermined wavelength is generated by a light source in the control device; conducted through a first optical fiber located at a transmitting side of the steering switch device to the optical operation switch secured to the steering wheel and, in turn, conducted through a second optical fiber located at a receiving side of the steering switch device to a photo sensor of the control device. The optical operation switch is adapted to be operated by a driver of the vehicle who supplies the control device with an optical operation signal.
Accordingly, in the discussed steering switch device, the fact that no power line is installed as a mobile part in the steering wheel in addition to the fact that the signal line is constituted with the optical fibers, without the need of any electrical connection between the mobile and stationary sides of the steering switch device, thus elimanates such conventional problems as aforementioned.
However, in the steering switch device according to the aforesaid Japanese Patent Lay-Open Print, a combination of photo couplers is used as the connection between a first pair of optical fibers extended at the side of the control device which is fixed to a vehicle body; and a second pair of optical fibers stretched from the mobile part at the side of the steering wheel, thereby forming a pair of routes. The respective optical fibers of both routes at the light transmission side and at the light reception side are thus required to have predetermined lengths thereof slacken in consideration of the steering quantity or angle of rotation of the steering wheel.
The two routes of optical fibers being thus slackened are always forced, though inherently having proper flexibility, to deform in a yielding manner or tensioned manner when the steering wheel is rotated.
To avoid such deformations of the optical fibers, a conceptual solution might well be taken that, an optical connection could be made between an optical fiber at the side of a control device and an optical fiber at the side of a steering wheel using an optical slip ring. However conventional optical slip rings as known are all impractical because they are structurally complicated and expensive, and have relatively low light transmission efficiencies.
In this respect, the present invention is designed effectively overcome conventional problems in the art, and particularly, such problems that are yet left unsolved even with the steering switch device according to the aforementioned Japanese Patent Lay-Open Print, that is, those problems concerning the durability as well as the efficiency of light transmission at a connecting part of an optical signal line between a control device on the stationary side and an operation switch on the mobile side.